Dry strength resin of amino/aldehyde acid colloid with acrylamide polymer, process for the production thereof and paper produced therefrom

ABSTRACT

Dry strength resins are prepared by reacting acrylamide polymers with amino/aldehyde resin acid colloids during the formation of the colloid. The resultant copolymers are useful as dry strength resins in the formation of paper.

This is a division of application, Ser. No. 892,654, filed Aug. 4, 1986,now U.S. Pat. No. 4,845,148.

BACKGROUND OF THE INVENTION

The treatment of paper-making fibers to render paper made therefromstronger has a long history of development. Many different chemicaladditives have been utilized for this purpose. Cationic starches areexemplary, but suffer from being inconsistent in performance,incompatible with other additives, etc. Amino-aldehyde resins have beenused to impart wet strength to paper both as resins per se and as acidcolloids thereof, see U.S. Pat. Nos. 2,345,543; 2,485,079; 2,485,080;2,559,220; 2,986,489.

In U.S. Pat. No. 3,594,271, there is disclosed the reaction product of awater-soluble starch and a melamineformaldehyde acid colloid as a drystrength imparting formaldehyde acid colloid as a dry strength impartingadditive for paper. This patent teaches the use of a partially or fullypolymerized (condensed) melamine-for-maldehyde resin in the formation ofthe acid colloid and the reaction of the acid colloid with the starch.While relatively effective, it never proved to be a commercial successbecause it was not as cost effective as existing products.

U.S. Pat. No. 4,461,858 discloses the manufacture and use of a polyvinylalcohol/melamine-formaldehyde resin acid colloid in the treatment ofpaper. The reaction product is said to impart increased processingcapability and improved wet and dry strength to the paper. The increasedprocessing capabilities are said to constitute easier process control,and better retention of fines. While the polyvinylalcohol/melamine-formaldehyde resin acid colloid products have achievedmoderate commercial success, they still leave something to be desired inthat they are very difficult to prepare in that the process iscumbersome and time consuming, they do not possess a very long storagelife, they are relatively expensive and they normally must be preparedat the site of the paper mill and at low solids.

SUMMARY OF THE INVENTION

It has now been discovered that the difficulties of prior dry strengthagents based on cationic amino-formaldehyde resins can be overcome andthe desired properties discussed above imparted to paper if theamino-formaldehyde resin is reacted with the acrylamide polymer in theform of an acid colloid while the acid colloid is being prepared.

The preparation of reaction products of acrylamide polymers andamino-aldehyde resins is taught in U.S. Pat. No. 2,852,901, herebyincorporated herein by reference. This patent teaches the preferredpreparation of the product by forming an aqueous solution of the acidcolloid of the amino-aldehyde resin beforehand and then reacting it withan aqueous solution of the acrylamide polymer. Other processes taughtfor the formation of the product involve the preparation of theamino-aldehyde resin in the presence of the acrylamide polymer, i.e.methylolating the acrylamide polymer with formaldehyde and then reactingwith cationic amine, etc. The patent fails to teach the addition of theacrylamide polymer to the amino-aldehyde resin acid colloid during theformation of the acid colloid.

DESCRIPTION OF THE INVENTION

INCLUDING PREFERRED EMBODIMENTS

As mentioned above, this invention resides in the formation of drystrength fibrous materials, the materials per se, a method for theformation of a dry-strength agent for use in the manufacture of fibrousmaterials and the dry strength agent composition per se. It specificallyrelates to the imparting of dry strength to felted, fibrous, cellulosicmaterials such as paper, board, shaped pulp articles and the like.

It is a principal object of the present invention to provide paper,board and other fibrous products by combining cellulosic fibers with anovel composition which imparts dry tensile strength and increasedinternal bonding strength thereto. The invention consists in part in theapplication of these compositions to water suspensions of hydrated orunhydrated cellulosic paper-making fiber pulp in the beater, stockchest, head box or at any other suitable point ahead of thepaper-forming step or the application of the compositions to the fibersof preformed paper as an aqueous spray or as a tub size, either alone orin admixture with other impregnating agents.

The term "paper", as used herein, is meant to include any cellulosicfiber-containing mat or web which is prepared by drawing down a diluteaqueous cellulose fiber suspension which may contain other fibrousmatter such as glass fiber, polyamide fiber, viscose fiber and the like.Examples include fabrics, felts, boards, shaped articles, etc.

We have found that the above and other objects are accomplished byapplying to fibrous, cellulosic material such as paper pulp, or thefibers of preformed paper, a copolymer of (1) an acid colloid of anamino/aldehyde resin and (2) an acrylamide polymer. We have found thatthese compositions are substantive to fibers of cellulosic material suchas paper pulp in aqueous suspension; i.e., the composition isselectively adsorbed or absorbed by the cellulosic fibers from a diluteaqueous solution or dispersion thereof containing these fibers. Thispermits the application to cellulosic fibers of sufficient quantities ofthe dry strength-imparting composition to produce the desired degree ofdry strength and internal bonding while the fibers are in dilute aqueoussuspensions of the consistency ordinarily used in paper mills, which isabout 0.1-6% or, in special processes, at higher consistencies.

The compositions of the present invention comprise an aqueous solutionof a copolymer of (1) a partially condensed, i.e., not fully condensed,water-soluble cationic thermosetting amino-aldehyde resin and (2) awater-soluble or water-dispersible, non-anionic acrylamide polymer, theratio of (1):(2) ranging from about 4:1 to about 1:4, respectively, thesolids of said solution being not more than about 20%, by weight, basedon the total weight of the solution, the molecular weight of theamino-aldehyde acid colloid portion of the copolymer being less than themolecular weight which is attained when an amino-aldehyde resin colloidis allowed to form completely, before reacting with the acrylamidepolymer. In general, the amount of solids preferred, is that amountwhich will not cause gelation to a stage of non-flowability.

The partially condensed, water-soluble, cationic, thermosetting,amino-aldehyde resin is in a colloidal state when reacted with theacrylamide polymer. It may have a molecular weight between about 500 and3,000,000 as disclosed in the above patents, which patents are herebyincorporated herein by reference. The preferred amino-aldehyde resinsare the melamino-formaldehyde resins, however, urea-formaldehyde;ammelide-formaldehyde resins, however, urea-formaldehyde;ammelide-formaldehyde; dicyandiamide-formaldehyde;biguanide-formaldehyde; urea-formaldehyde polyalkylene polyamine;polyureido, etc., resins can also be utilized to form the novelcompositions of the present invention. These resins contain sufficientaldehyde for reaction with the carboxamide groups of the acrylamidepolymer. Both the unalkylated and alkylated varieties of theamino-aldehyde resins can be employed. From 1-6 mols of combinedaldehyde, preferably 205, and more preferably about 3, per mol of aminocompound are used. The resins may be alkylated with 1-6 mols a loweralkyl alcohol to stabilize the resin at high solids before the acidcolloid formation.

The acid colloids of amino-aldehyde resins are well known to thoseskilled in the art and further discussion thereof can be found in TAPPIMonograph Series No. 29; "Wet Strength Paper and Paperboard"; JohnWeidner, Editor; Tech. Assoc. of the Pulp and Paper Industry, N.Y.C.;1965, pages 20-32.

The water-soluble or water-dispersible, non-anionic acrylamide polymersuseful herein include those homopolymers prepared from acrylamide,methacrylamide, itaconamide, N-alkyl acrylamides, N-alkylmethacrylamides; copolymers of these acrylamides with not more than 50%,preferably not more than 25%, by weight, based on the total weight ofpolymer, of such non-ionic comonomers as styrene, vinyl chloride, vinylacetate, methyl acrylate, acrylonitrile, and the like. As mentionedabove, the acrylamide polymer must be non-anionic, i.e. cationic ornon-ionic. Small amounts, however, of anionic comonomers (i.e., up toabout 2%), such as acrylic acid may be tolerated. Cationic monomers suchas dimethylaminoethyl acrylate; diallyldimethyl ammonium chloride;methacrylamidopropyl trimethyl ammonium chloride; and the like may beused in amounts up to about 10%, by weight, same basis, especially whenthere is a high cationicity demand because of the furnish employed or ifthe paper making process is conducted at neutral or alkaline pH. Thepresence of the cationic comonomer which causes this increasedcationicty increases the retention of the compositions of the presentinvention to the paper-making fibers. The molecular weight of theacrylamide polymer should range from about 40,000 to about 500,000,preferably from about 75,000 to about 300,000.

The ratio of the amino-aldehyde resin acid colloid to the acrylamidepolymer should range from about 4:1 to about 1:4, preferably from about2:1 to about 1:2, respectively.

The stability of the compositions of the present invention are governedby the solids content thereof. The compositions may be used immediately,i.e., within 15 minutes as produced for imparting dry strength to, e.g,paper at about 20% solids level, however, they are more practicallyemployed sometime after production, i.e, after packaging and shipping tothe consumer. At about 8% solids, by weight, based on the weight of thecomposition, the composition is stable for 48 hours and at about 5%solids it is stable for about 120 hours. Infinite stability is shown atless than about 3% solids.

The amino aldehyde resin acid colloid, as a reaction product with theacrylamide polymer, has a molecular weight lower than that molecularweight which is attained when the acid colloid is allowed to formcompletely before reacting with the acrylamide polymer. That is to say,it is essential when producing the novel compositions of the presentinvention that the acrylamide polymer be reacted with the acid colloidduring the formation of the acid colloid. The compositions hereof do notexhibit their unusual properties unless this is done, i.e., addition ofsolutions of the completed acid colloid and the acrylamide polymer;formation of the acid colloid in the presence of the acrylamide polymerab initio or formation of the amino-aldehyde resin and the acid colloidthereof in the presence of the acrylamide polymer ab initio do notproduce satisfactory compositions. Suitable aldehydes besideformaldehyde include acetaldehyde, propionaldehyde, crotonaldehyde,glutaraldehyde and others known to form resins with, for example,triazines. The result of the addition of the acrylamide polymer to theacid colloid during the formation of the acid colloid, while not wishingto be bound by any theory, is that while the colloid is forming, theformed colloid is free to react with the acrylamide polymer immediately.The result is that shorter, but more, chains of the acid colloid reactwith the acrylamide polymer. Thus, the molecular weight of the graftedacid colloid portion of the final composition is less than a fullycompleted acid colloid. It is believed that this uniform, more frequentnumber of acid colloid segments in the final composition results in theunique properties of the instant compositions.

The acrylamide polymer may be added to the amino-aldehyde resinpreferably as an aqueous solution or in the form of a dry powder. Asdiscussed above, however it must be added after the acid colloid hasbegun to form, i.e, after a charge is created on the amino-aldehyderesin by the acid. The compositions of the present invention may beformed by a batch or continuous process.

The novel process of the present invention comprises reacting one moleof a triazine contained in a partially condensed, water-soluble,thermosetting amino-aldehyde resin, in aqueous solution, with from about0.35 to about 1.5 mol of an acid, under conditions to initiate acidcolloid formation but for a period of time insufficient to form acompleted acid colloid of said amino-aldehyde resin, and then reacting awater-soluble or water-dispersible, non-anionic acrylamide polymer withsaid incompletely formed acid colloid for from about 0.5 to about 150minutes at a temperature ranging from about 40° C. to about 100° C., theratio of said acrylamide polymer to said incomplete acid colloid rangingfrom about 4:1 to about 1:4, respectively, the total solids contentbeing not more than about 20%, by weight, based on the weight of thereaction media.

Under the conditions employed during the acid colloid preparation, acidcolloid formation begins as evidenced by a build-up of charge or drop inpH or, or the formation of the familiar blue haze normally observedduring such a reaction. Generally, a temperature ranging from about 50°C. to about 100° C. and a reaction time of from about 15 seconds to 45minutes are employed. We have found that higher temperatures requirelesser reaction times, i.e, at about 80° C. to about 100° C. thereaction occurs in about 15 seconds to 5 minutes whereas at about 50° C.to about 80° C., from about 5 minutes to 45 minutes is required.Vigorous agitation is useful but not required.

The acids employed to form the acid colloid of the amino-aldehyde resinare well known in the art and include nitric acid, phosphoric acid,lactic acid, hydrochloric acid, citric acid and the like. Hydrochloricacid is preferred. The amount of acid added per mole of amino compoundis dependent upon the specific acid used. However, generally from about0.35 to about 1.5 mol of acid per mol of amino compound is sufficient.For example, hydrochloric acid is effective at 0.35-0.80 mol per mol ofamino compound; phosphoric acid is useful at 0.6-1.5 mols per mol ofamino compound and nitric acid functions satisfactorily at 0.6-1.0 molper mole of amino compound. Sulfuric acid is not useful herein becauseit forms an insoluble sulfate salt with the amino compound. A pH rangingfrom about 1.0 to about 5.0, preferably from about 1.5 to about 3.0 isnormally employed. Dilution to the solids content described above withwater follows.

The products produced by the above-described process constitute theunique compositions of this invention.

The novel compositions of the present invention are effective as drystrength agents over a pH of about 4.0 to about 9.0. They are effectivewith all types of virgin pulp and also recycled pulp includinggroundwood grades, print grades, linerboard pulp, corrugating medium;waste paper pulps, high ash pulps, filled publication paper pulps; andfine paper grades. They are effective in the presence of fillers andresidual pulping chemicals.

The novel compositions of this invention can be applied to paperproducts by tub application methods if desired. Thus, for example,preformed and completely or partially dried paper prepared from achemical pulp such as sulfite pulp, sulfate pulp or a mechanical pulpsuch as goundwood or any mixture thereof may be immersed in or sprayedwith a 1% to 5% aqueous solution or dispersion of the composition andimpreganted with about 50-100% thereof, based on the weight of thepaper. The paper may then be heated for about 0.1 to 60 minutes attemperatures, whereby the paper is dried and polymer-bonding of thefibrils thereof is developed. The resulting paper has increased drystrength, and therefore this method is well suited for the impregnationof stock such as kraft wrapping paper, bag paper board grades and thelike.

However, because of the substantive properties of the compositions forcellulosic fibers, i.e., they are water-soluble or water-dispersibleunder the conditions normally used in preparing paper furnishes,including those containing calcium carbonate or other alkaline sizingmaterials, they deposit selectively by adsorption or absorption on thefibers of cellulosic paper stock. Accordingly, the compositions may bedissolved in an aqueous suspension of the paper stock and added theretoas an aqueous solution, and this addition may be made in the beater,stock chest, Jordan engine, fan pump, head box or at any other suitablepoint ahead of the papermaking wire or screen, followed by forming thetreated fibers into a felted product on the wire or cylinder. The novelcompositions hereof may be used in conjunction with other common paperadditives such as rosin, ASA or ketene dimer sizes, anti-foams,anti-microbial agents and the like. Frequently, synergism is noted insuch conjoint use, e.g. the sizing imparted by rosin size may beenhanced in their presence.

The pH of the pulp suspension at the point of addition of thecomposition is not critical and may be any value between about 4 and 9,thus, the process tolerates the presence of alkaline reacting fillerssuch as calcium carbonate. Optimum strength is generally developed at apH of between about 4.2 and 7.5 so that, if desired, the process may beperformed wholly on the alkaline side. Although appreciable dry strengthis noted when as little as 0.1% of the polymer is adsorbed in thismanner, it is ordinarily advisable to apply quantities within the rangeof about 0.15% to 5% or more of the composition solids based on the dryweight of the paper stock.

After adding and incorporating the composition into the furnish andforming the paper, the felted product is preferably heated for about 0.1to 60 minutes at 75°-300° F. In the usual manner to evaporate watertherefrom. This heating also increases or further develops the bondbetween the cellulosic fibrils that results in dry strength in thefinished product.

The following examples are set forth for purposes of illustration onlyand are not to be construed as limitations on the present inventionexcept as set forth in the appended claims. All parts and percentagesare by weight unless otherwise specified.

The term "standard viscosity," as used herein, means the viscosity of a0.1% solution of the polymer in 1M NaCl in centipoise measured on aBrookfield Viscometer with UL adapter, speed 60 rpm, 25° C.

EXAMPLE 1 (Comparative)

Example 1 of U.S. Pat. No. 2,862,901 is followed explicitly except thatin one instance, A) PAREZ®-707 resin, a methylated trimethylolmelaminemanufactured by American Cyanamid Company, is used and in a secondinstance B) PAREZ®-607 resin, a powder form of trimethylol melamine, isemployed.

Handsheets are prepared from a furnish comprising 50% white, blank newsrepulped until chip-free and then blended with beaten bleached softwoodKraft/bleached hardwood Kraft and mixed with the products produced asdescribed above. The pH is 6.5. The resultant paper is tested forinternal bond and bursting strength by standard TAPPI methods. Theresults are set forth in Table I below.

                  TABLE I                                                         ______________________________________                                                          Bursting Strength                                                                           Internal Bond                                 Example                                                                              Treatment  (lb/in.sup.2) (ft-lbs × 10.sup.-3)                    ______________________________________                                        1A     6 lbs/ton  43.6          148                                                  9 lbs/ton  45.7          156                                           1B     6 lbs/ton  43.0          136                                                  9 lbs/ton  46.0          163                                           Blank #1                                                                             --         42.4          124                                           Blank #2                                                                             --         43.1          133                                           ______________________________________                                    

As can be seen, the products produced by the process of U.S. Pat. No.2,862,901 provide little, if any, increase in bursting strength and amoderate increase in internal bonding.

EXAMPLE 2

To a suitable reaction vessel are charged 258.25 parts of deionizedwater. A second vessel is then charged with 4.25 parts of concentratedhydrochloric acid, a third vessel with 37.5 parts of methylatedtrimethylolmelamine at 80% solids and to a fourth vessel 150.0 parts ofa 10% solution of polyacrylamide of a molecular weight of about 200,000.All the vessels are heated to about 95° C. in a steam bath. The contentsof the first vessel are slowly agitated while adding the contents ofvessels two and three thereto. Agitation is increased and the contentsof the first vessel are stirred for 30 seconds. While an acid colloid ofthe methylated trimethylolmelamine is forming, 150.0 parts thereof areremoved and the polyacrylamide of vessel four is immediately added tothe remaining partially formed acid colloid. Stirring thereof for 30seconds is accomplished and 300 parts of deionized water are added todilute the composition and stop the reaction and result in CompositionA. To the 150.0 parts of removed acid colloid are added immediately150.0 parts of deionized water to form Product B. The resultantComposition B has a faint haze. The molecular weight of the acid colloidof Composition B is higher than that of the acid colloid of CompositionA. Composition B is not as effective in producing wet strength whenapplied to the paper-making fibers as in Example 1 as commerciallyavailable acid colloids.

When Product A is applied to the paper-making fibers as in Example 1,the Bursting Strength recorded is 49.2 lbs/in² at 6 pounds per ton and50.4 lbs/in² at 9 pounds per ton. The Internal Bond is 174×10⁻³ ft. -lbat 6 pounds per ton and 221×10⁻³ ft. -lb at 9 pounds per ton.

EXAMPLE 3

To a suitable reaction vessel are added 258.0 parts of water and 4.25parts of concentrated hydrochloric acid. The solution is heated to 90°C. and 37.5 parts of PAREZ® 707 (80.0% solids), methylated trimethylolmelamine (M/F) are added slowly with stirring. The agitation isincreased for 30 seconds. Acid colloid formation begins as evidenced bythe formation of a slight blue haze. 300 Parts of a 10% aqueous solutionof non-ionic polyacrylamide (PAM) having a molecular weight of about290,000 are added before acid colloid formation is complete. High speedstirring is continued for an additional 30 seconds resulting in a 10%solution of melamine/formaldehyde acid colloid and polyacrylamide at aratio of 1:1. The reaction is quenched by pouring it over 600 parts ofice and the resultant composition is diluted to 1% solids with water.The product is designated "Product A".

Following the teachings of U.S. Pat. No. 4,461,858, a cationicinteraction product is made from polyvinyl alcohol (PVA), Elvanol 71-30made by DuPont de Nemours and Company and a melamine/formaldehyde acidcolloid made from PAREZ® 707. This product is designated as "Product B".

The above products are both tested for their ability to impart drystrength to paper by adding them to a 0.6% consistency slurry of refinedpaper pulp. The first pulp designated "Pulp #1", is a 50/50 mixture ofbleached hardwood kraft/bleached softwood draft containing no filler andadjusted to pH 4.5. The second pulp, "Pulp #2," is the same fiber mixbut additionally contain 10% clay and is adjusted pH 6.5. Both furnishesare adjusted to 50 ppm Ca⁺⁺ by the addition of CaCl₂ and to 200 ppm SO₄⁼ by the addition of Na₂ SO₄. Appropriate amounts of resins are added tothe pulps as indicated below and 70 pound basis weight handsheets areformed on a Noble A Wood handsheet machine. Dilution water for thedeckle of the machine is deionized water treated with 50 ppm Ca⁺⁺, 200ppm SO₄ ⁼ and adjusted to pH 4.5 or 6.5 as the case may be. The sheetsare pressed and dried on the machine and then given a slight pose cureof 3 minutes in an oven at 105° C. The results are set forth in Table 2,below. Additional data employing normal M/F resin alone (M/F) is alsopresented along with data obtained using a polyvinyl alcohol producedaccording to the process of the present invention. All such products aremarked*.

                                      TABLE 2                                     __________________________________________________________________________                            Tensile Internal                                                  Amount  Burst                                                                             Dry Wet Bond    Clay                                  Example                                                                            Additive                                                                             (lb/ton)                                                                           Pulp                                                                             (lb/in.sup.2)                                                                     (lb/in)                                                                           (lb/in)                                                                           (ft/lb × 10.sup.-3)                                                             (%)                                   __________________________________________________________________________    --   Blank  --   #1 43.7                                                                              25.7                                                                              1.38                                                                              --      --                                    3A   M/F    10   #1 57.1                                                                              30.5                                                                              5.54                                                                              --      --                                         M/F    20   #1 63.3                                                                              28.7                                                                              6.76                                                                              --      --                                         M/F    30   #1 65.9                                                                              32.2                                                                              7.47                                                                              --      --                                    3B   M/F*   10   #1 53.4                                                                              30.9                                                                              4.83                                                                              --      --                                         M/F*   20   #1 59.1                                                                              24.9                                                                              6.26                                                                              --      --                                         M/F*   30   #1 61.9                                                                              27.2                                                                              7.01                                                                              --      --                                    3C   Product B                                                                            10   #1 54.0                                                                              25.5                                                                              3.49                                                                              --      --                                         Product B                                                                            20   #1 57.4                                                                              29.6                                                                              4.86                                                                              --      --                                         Product B                                                                            30   #1 60.2                                                                              26.4                                                                              5.73                                                                              --      --                                    3D   PVA/MF*                                                                              10   #1 56.1                                                                              22.2                                                                              3.54                                                                              --      --                                         PVA/MF*                                                                              20   #1 57.6                                                                              32.2                                                                              5.49                                                                              --      --                                         PVA/MF*                                                                              30   #1 65.3                                                                              32.8                                                                              5.82                                                                              --      --                                    3E   Product A                                                                            10   #1 62.2                                                                              30.9                                                                              4.93                                                                              --      --                                         Product A                                                                            20   #1 69.1                                                                              34.3                                                                              5.95                                                                              --      --                                         Product A                                                                            30   #1 70.4                                                                              35.0                                                                              6.65                                                                              --      --                                    --   Blank  --   #2 42.0                                                                              24.1                                                                              1.18                                                                              83      1.17                                  3F   Product B                                                                            10   #2 46.5                                                                              24.8                                                                              2.07                                                                              99      2.87                                       Product B                                                                            20   #2 52.9                                                                              30.0                                                                              3.17                                                                              138     2.84                                       Product B                                                                            30   #2 56.9                                                                              33.5                                                                              4.74                                                                              169     2.41                                  3G   Product A                                                                            10   #2 53.4                                                                              30.0                                                                              3.26                                                                              92      6.33                                       Product A                                                                            20   #2 58.9                                                                              32.6                                                                              3.78                                                                              147     5.41                                       Product A                                                                            30   #2 63.3                                                                              35.5                                                                              4.06                                                                              180     4.69                                  3H   PAM/MF*.sup.1                                                                        10   #2 43.3                                                                              26.8                                                                              1.99                                                                              73      4.41                                       PAM/MF*.sup.1                                                                        20   #2 48.2                                                                              27.9                                                                              2.39                                                                              71      4.88                                       PAM/MF*.sup.1                                                                        30   #2 49.2                                                                              29.1                                                                              2.77                                                                              93      4.79                                  3I   PAM/MF*.sup.2                                                                        10   #2 42.9                                                                              24.5                                                                              1.90                                                                              61      5.77                                       PAM/MF*.sup.2                                                                        20   #2 48.1                                                                              27.5                                                                              2.89                                                                              91      6.21                                       PAM/MF*.sup.2                                                                        30   #2 69.2                                                                              28.4                                                                              3.24                                                                              113     6.27                                  __________________________________________________________________________     .sup.1 ratio 2:1, respectively                                                .sup.2 ratio 1:2, respectively                                                The increase in clay retained in the sheet by Product A as compared with      Product B should be noted. Improved retention is a valuable side effect o     the compositions of this invention. Furthermore, the increase in clay         content is achieved without the normal weakening of the sheet usually         attendant increased filler content.                                      

EXAMPLE 4

The procedure of Example 3 for the production of the Product A isrepeated twice. Handsheets are prepared from these products ("Product C"and Product D") and compared to sheets prepared from other dry strengthadditives. The results are set forth in Table 3.

The handsheets are made using mill white water in the sump andrecirculation. The pH is 6.6. The mill stock has a freeness of 78 ml.CSF and a fines content of 0.17%. The basis weight of the handsheetsformed is 35 lbs. The first three discard sheets in each set are heavydue to retention of fines from the white water, and are slow to drain.The lowest treatment level is made first and the water remaining fromthis set is used for the next higher level. Only one discard sheet ismade for the second and subsequent sets with that additive. Sheets arepressed between two blotters with 21/2 pound weights and dried 35seconds at 240° F. The sheets are cured 3 minutes at 105° C. beforeconditioning.

The starch/MF product is made by cooking a low molecular weight slightlyethylated, modified, commercially available starch at 10% solids andreacting the hot solution with an equal volume of hot 10% M/F resin acidcolloid. After 5 minutes, the resultant product is diluted to 1% withcold water.

The PVA/MF product employed in this and following examples is acommercially available material from DuPont de Nemours Co. at 1% solids.

Mullen burst tests are made on doubled sheets because of the weakness ofthe stock, which is 100% recycled news. Tensile and internal bond testsare made by standard methods.

                  TABLE 3                                                         ______________________________________                                                                                 Dry                                  Exam-           Amount   Burst Internal Bond                                                                           Tensile                              ple   Additive  (lb/ton) (lb/in.sup.2)                                                                       (ft-lbs × 10.sup.-3)                                                              (lbs/in)                             ______________________________________                                        --    Blank     --       11.75 24        8.03                                 4A    PVA/MF    3        13.40 22        9.43                                       PVA/MF    6        11.40 22        8.08                                       PVA/MF    9        12.50 28        8.38                                       PVA/MF    12       12.40 33        8.63                                 4B    Product C 3        13.20 23        9.29                                       Product C 6        13.30 30        8.22                                       Product C 9        14.50 48        9.63                                       Product C 12       14.70 59        9.70                                 4C    Product D 3        11.90 21        8.35                                       Product D 6        12.60 27        8.85                                       Product D 9        13.40 37        9.88                                       Product D 12       15.20 52        11.37                                      Starch/MF 3        12.70 31        8.32                                       Starch/MF 3        11.80 18        8.91                                       Starch/MF 9        11.60 22        8.14                                       Starch/MF 12       11.90 24        8.85                                 ______________________________________                                    

EXAMPLE 5

The procedure of Example 3 for the production of Product A is repeatedthrice. Handsheets are prepared from these products ("Products E, F andG") and compared to sheets prepared from other dry strength additives.The results are set forth in Table 4.

Unbleached kraft is beaten for 45 minutes to 500 ml. CSF andequilibrated overnight with 3% black liquor solids. Pulp and dilutionwater are treated with 200 ppm⁼ SO₄ Standard single pass handsheets aremade at 70 pounds basis weight and tested by standard methods. Alum isused at 15 lb/ton. The pH is 5.0. This furnish is designated "Pulp C."

Rotogravure furnish containing 47% bleached kraft, 35% groundwood and18% TMP is designated "Pulp D". With this furnish 15 lb/ton of alum isused and 15 lb/ton of sodium aluminate. Pulp and dilution water istreated with 200 ppm SO₄ ⁼ and 50 ppm Ca⁺⁺. The pH is 4.5.

                  TABLE 4                                                         ______________________________________                                                                            Internal                                                                      Bond   Dry                                Exam-           Amount        Burst (ft-lb ×                                                                       Tensile                            ple   Additive  (lb/ton) Pulp (lb/in.sup.2)                                                                       10.sup.-3)                                                                           (lb/in)                            ______________________________________                                        --    Blank     --       C    57.6  65     31.74                              5A    Product E 3        C    62.3  79     35.99                                    Product E 6        C    61.3  78     38.31                                    Product E 9        C    63.1  78     37.22                                    Product E 12       C    60.9  85     32.73                                    Product E 15       C    64.7  89     32.65                              5B    Product F 3        C    61.6  74     36.37                                    Product F 6        C    59.1  77     35.90                                    Product F 9        C    61.5  91     34.94                                    Product F 12       C    62.9  70     35.81                                    Product F 15       C    65.9  63     34.52                              5C    Product G 3        C    58.2  69     34.70                                    Product G 6        C    58.9  68     34.51                                    Product G 9        C    62.4  63     36.07                                    Product G 12       C    59.8  63     34.03                                    Product G 15       C    60.9  58     34.59                              5D    PVA/MF    3        C    57.2  62     33.93                                    PVA/MF    6        C    58.1  62     34.95                                    PVA/MF    9        C    57.8  57     35.20                                    PVA/MF    12       C    58.6  51     34.42                                    PVA/MF    15       C    57.9  60     35.06                                    Blank     --       --   71.65 162    40.6                               5E    PVA/MF    3        D    75.0  160    36.9                                     PVA/MF    6        D    75.8  158    46.6                                     PVA/MF    9        D    74.8  122    42.4                                     PVA/MF    12       D    75.4  130    45.9                                     PVA/MF    15       D    76.8  161    43.4                               5F    Product E 3        D    74.0  127    39.8                                     Product E 6        D    77.4  155    41.5                                     Product E 9        D    77.9  154    45.1                                     Product E 12       D    81.6  172    46.0                                     Product E 15       D    80.0  196    40.2                               5G    Product F 3        D    75.3  156    46.4                                     Product F 6        D    77.6  195    43.2                                     Product F 9        D    81.1  176    45.0                                     Product F 12       D    79.6  217    45.2                                     Product F 15       D    81.0  211    41.7                               ______________________________________                                    

EXAMPLE 6

Paper stock from an operating paper mill making fine paper is diluted to0.6% and treated with 60 pounds per ton of alum and adjusted to pH 4.5which are the conditions of mill use. The resultant stock is treatedwith "Product H", a polyacrylamide--M/F resin/acid colloid copolymerprepared as in Example 3 for Product A and formed into 70 pound basisweight handsheets. Comparisons to commerically available products arealso made. The results are set forth in Table 5. The Fold tests areconducted on an M.I.T. fold tester; double folds; 2 lb. load. "Product85" is a commerically available acrylamide/acrylic acid (90/10)copolymer.

                  TABLE 5                                                         ______________________________________                                                         Amount   Burst Internal Bond                                 Example                                                                              Additive  (lb/ton) (lb/in.sup.2)                                                                       (ft-lb × 10.sup.-3)                                                               Fold                                ______________________________________                                        --     Blank     --       41.8  111        84.3                               6A     Product H 5        56.3  226       260.1                                      Product H 10       63.8  360       555.6                                      Product H 15       67.9  387       894.9                               6B     Product 85                                                                              5        50.1  188       165.9                                      Product 85                                                                              10       54.4  205       241.1                                      Product 85                                                                              15       57.1  236       313.4                               6C     M/F Acid  5        48.1  158       140.5                                      Colloid                                                                       M/F Acid  10       52.7  187       205.5                                      Colloid                                                                       M/F Acid  15       57.4  195       285.5                                      Colloid                                                                ______________________________________                                    

EXAMPLE 7

A 40% softwood, 30% hardwood, 30% RMP pulp is diluted to 0.6%consistency with mill white water and heated with alum and additive andadjusted to pH 4.7. Six British handsheets are made and pressed underTAPPI conditions, oven dried to 5% moisture, equilibrated under TAPPIconditions, weighed and tested.

"Product I" is a copolymer of the present invention prepared as inExample 3 for Product A. "Commercial A" is a commercially availableMannich quaternization product of polyacrylamide. "Commercial B" is acommercially available glyoxalated acrylamide/ diallyldimethylammononiumchloride copolymer blended with a quaternized epichlorohydrin/aminereaction product. "Commercial C" is a commercially available glyoxalatedacrylamide/diallyldimethylammonium chloride copolymer. "Commercial D" isthe same as Product 85, Example 6. "Commercial E" is a commerciallyavailable poly(ampholytic starch). The starch is slurred at 3% andcooked at the boil for 30 minutes with cationizing reagent at ambientpH. The laboratory results are set forth in Table 6. The burst tests areconducted in both the mill and the laboratory.

                                      TABLE 6                                     __________________________________________________________________________                          Burst                                                                Amount                                                                             Caliper                                                                           (lb/in.sup.2)                                                                       Internal Bond                                                                        Bulk                                       Example                                                                            Additive                                                                              (lb/ton)                                                                           Mils                                                                              Mill                                                                             Lab                                                                              (ft-lbs × 10.sup.3)                                                            cc/g.                                      __________________________________________________________________________    --   Blank    5   5.2 38.2                                                                             38.6                                                                              94    1.88                                       7A   Product I                                                                              5   4.7 41.5                                                                             43.2                                                                             137    1.77                                            Product I                                                                             10   5.0 41.1                                                                             44.1                                                                             156    1.75                                            Product I                                                                             15   4.8 45.5                                                                             46.1                                                                             167    1.68                                       7B   Commercial A                                                                           5   5.4 37.0                                                                             36.6                                                                              96    1.87                                            Commercial A                                                                          10   5.6 37.8                                                                             40.6                                                                              88    1.87                                            Commercial A                                                                          15   5.7 40.0                                                                             37.2                                                                              95    1.86                                       7C   Commercial B                                                                           5   5.6 41.8                                                                             39.9                                                                              70    1.87                                            Commercial B                                                                          10   5.6 43.3                                                                             41.1                                                                              92    1.87                                            Commercial B                                                                          15   5.5 42.2                                                                             41.7                                                                             104    1.86                                       7D   Commercial C                                                                           5   5.5 41.4                                                                             41.1                                                                              96    1.85                                            Commercial C                                                                          10   5.6 39.5                                                                             40.5                                                                             105    1.82                                            Commercial C                                                                          15   6.0 40.1                                                                             43.2                                                                             145    1.93                                       7E   Commercial D                                                                           5   5.6 37.9                                                                             38.2                                                                             101    1.88                                            Commercial D                                                                          10   6.4 36.3                                                                             37.6                                                                              89    2.12                                            Commercial D                                                                          15   6.1 37.3                                                                             37.3                                                                              84    2.03                                       7F   Commercial E                                                                          10   6.5 39.2                                                                             41.6                                                                             119    2.07                                            Commercial E                                                                          20   6.1 42.3                                                                             40.4                                                                             131    1.94                                            Commercial E                                                                          30   5.9 44.8                                                                             45.4                                                                             181    1.88                                       __________________________________________________________________________

A sample of Product A produced in Example 3 is added to long-fiberedcotton pulp, at a pH of 4.2, along with 40 pounds per ton of alum.Handsheets are formed from the resultant pulp and tested. The resultsare set forth in Table 7. Fold tests are conducted as in Example 6.

                  TABLE 7                                                         ______________________________________                                               Additive                                                                      Amount          Tensile (lb/in)                                        Example  (lb/ton)   Fold   Dry     Wet   Tear                                 ______________________________________                                        --       Blank      17.8   2.70    0.41  105                                  8A       20          387   4.43    1.21  120                                  8B       45         1452   6.77    1.95  114                                  8C       90         2340   7.26    2.0   110                                  ______________________________________                                    

Formation is noted as adversly affected, probably due to the use of along-fibered pulp stock.

In a subsequent trial on a commercial paper machine, paper of excellentquality with exceptionally high folding endurance and erasability ismade.

EXAMPLE 9

To a suitable reaction vessel are charged 250 parts of a 10% aqueouspolyacrylamide solution (MW=150,000) and 204 parts of deionized water.The solution is heated to 60° C. and 8.5 parts of hydrochloric acid areadded over a period of one minute. Thirty-seven parts ofmelamine/formaldehyde are added slowly and the viscosity is monitoredover 43 minutes until a Shell cup viscosity of 28.45 seconds isattained. The reaction is then terminated by adding 250 parts of colddeionized water. The resultant solution is then diluted to 2% solids andtested as a dry strength agent identified as "Comparative A", by addingto a paper pulp to drawing down handsheets therefrom. The results areset forth in Table 8 and compared to a commercially available cationicpolyacrylamide/glyoxal resin designated "Resin A" and to a copolymer ofthe process of the present invention prepared as for Product A inExample 3 and identified as "Product J".

                  TABLE 8                                                         ______________________________________                                                                                 Dry                                                  Amount   Burst Internal Bond                                                                           Tensile                              Example                                                                              Additive (lb/ton) (lb/in.sup.2)                                                                       (ft-lb × 10.sup.-3)                                                               (lb/in)                              ______________________________________                                        --     Blank    --       40.4   65       23.51                                9A     Resin A  6        57.5  130       31.50                                       Resin A  9        64.2  152       34.31                                       Resin A  12       68.0  170       33.81                                9B     Product J                                                                              6        59.7  129       29.26                                       Product J                                                                              9        58.6  132       29.47                                       Product J                                                                              12       62.2  169       30.04                                9C     Compara- 6        55.4  101       29.37                                       tive A                                                                        Compara- 9        56.0  110       29.31                                       tive A                                                                        Compara- 12       60.7  115       29.66                                       tive A                                                                 ______________________________________                                    

EXAMPLES 10 and 11

The procedure of Example 3 is again followed except that the ratio ofthe amino-aldehyde resin to the acrylamide polymer ranges 10) from about4:1, respectively, and 11) from about 1:4, respectively. In eachinstance, similar results are obtained.

EXAMPLE 12

The procedure of Example 2 is followed except that the polyacrylamide isreplaced by a 80/20 copolymer of acrylamide and acrylonitile, molecularweight 342,000. Similar results are observed.

EXAMPLE 13

Example 12 is repeated in all essential details except that a copolymerof methacrylamide and styrene (90/10) is employed. The molecular weightis 400,000. Again, excellent results are achieved.

EXAMPLE 14

When the procedure of Example 3 is followed except that thepolyacrylamide has a molecular weight of only 32,000, poor resultsoccur.

EXAMPLE 15

The procedure of Example 2 is followed except that nitric acid isemployed in lieu of the hydrochloric acid thereof. The mol ratio ofnitric acid to melamine is 0.8:1.0, respectively. Excellent results areachieved.

EXAMPLE 16

When phosphoric acid is used in place of the hydrochloric acid ofExample 2, substantially identical results are recorded. The mol ratioof phosphoric acid to melamine is 13:1, respectively.

EXAMPLE 17

Replacement of the melamine/formaldehyde resin of Example 2 with anon-alkylated melamine/formaldehyde resin results in substantially thesame as shown therein.

EXAMPLE 18

A furnish comprised of a 50/50 mixture of hardwood-softwood bleachedkraft is adjusted to a pH of 6.5. The Ca⁺⁺ content is adjusted to 50 ppmand the SO₄ ⁼ content to 200 ppm. To the resultant furnish are addedvarious amounts of an acrylamide polymer--M/F resin acid colloidcopolymer prepared as in Example 3 (Product A) wherein the acrylamidepolymer is a copolymer of acrylamide and dimethylaminoethyl acrylatequaternized with methyl chloride (90/10). The results are set forth inTable 9.

                  TABLE 9                                                         ______________________________________                                        Amount of             Internal    Tensile                                     Copolymer         Burst   Bond      Dry   Wet                                 (lb/ton)                                                                              Mobility  (lb/in.sup.2)                                                                         (ft/lbs × 10.sup.-3)                                                              (lb/in)                                   ______________________________________                                        Control -0.89     50.3     74       28.11 0.51                                3.0     -0.59     57.3    104       31.29 1.21                                6.0      0.00     55.0    107       30.65 1.42                                9.0     +0.24     61.3    123       30.88 1.74                                12.0    +0.51     61.5    129       30.63 2.04                                ______________________________________                                    

EXAMPLE 19

Following the procedure of Example 18 except that a 3.0 lb/ton additionis not used, the following results are achieved.

For 6, 9 and 12 pounds of additive copolymer per ton the Burst is 60.2;62.3; 63.8 lbs/in², respectively, the Internal Bond is 115; 112; 115ft./lbs.×10⁻³, respectively, and the Dry Tensile is 31.27; 31.15; 33.59lb/in, respectively. The respective values for the Control are 48.7;67.0 and 25.95.

EXAMPLE 20

Standard newsprint furnish is charged to a standard Fourdrinierpaper-making machine at a rate of 21 tons per hour. The machine isrunning at a paper-making speed of 2500 ft./min. The pH of the furnishis 4.5 and contains 17.0 pounds per ton of alum. Product A of Example 3is added as a 2% aqueous solution to the thick stock entering the blendchest. The machine is monitored over a two day period. The results areset forth in Table 10, below. The PVA/MF is the same as that of Example4.

                  TABLE 10                                                        ______________________________________                                                                           Internal Bond                                      Amount              Burst  (ft/lbs ×                            Additive                                                                              lb/ton    Time      (lb/in.sup.2)                                                                        10.sup.-3)                                 ______________________________________                                        Control --        --          10.1    80                                      Control --        --           9.8    90                                      PVA/MF  10        10:55  AM   10.4   114                                      PVA/MF  10        11:40  AM   10.6   118                                      PVA/MF  10        12:30  PM   10.5   112                                      PVA/MF  10        1:15   PM   10.7   107                                      Product A started at 1:45 → → →                          Product A                                                                             4         2:00   PM   10.4   106                                      Product A                                                                             4         2:55   PM   11.4   113                                      Product A                                                                             4         3:55   PM   10.4   107                                      Product A - Amount changed to 6 at 4:05 PM                                    Product A                                                                             6         4:25   PM   10.9   114                                      Product A                                                                             6         5:15   PM   10.2   113                                      Product A                                                                             6         6:05   PM   10.9   137                                      Product A - Amount changed to 8 at 6:20 PM                                    Product A                                                                             8         7:25   PM   10.8   130                                      Product A                                                                             8         9:10   PM   11.3   123                                      Product A                                                                             8         10:10  PM   10.9   128                                      Product A                                                                             8         11:10  PM   11.9   129                                      Product A                                                                             8         12:10  AM   11.1   128                                      Product A                                                                             8         1:05   AM   11.1   119                                      Product A                                                                             8         1:50   AM   10.8   138                                      Product A                                                                             8         2:40   AM   10.8   135                                      Product A                                                                             8         3:30   AM   11.1   136                                      Product A                                                                             8         4.25   AM   10.2   129                                      Product A                                                                             8         5:40   AM   11.0   132                                      Product A                                                                             8         6:30   AM   10.9   130                                      Product A                                                                             8         7:10   AM   10.2   122                                      Product A - amount changed to 10 at 7:25 AM                                   Product A                                                                             10        8:10   AM   10.7   125                                      ______________________________________                                    

The advantages of the copolymer of the present invention are many. Forexample, it is possible to match the product needs of any specific papermill by varying the amount of acrylamide polymer and/or amino-aldehyderesin. The specific products can be prepared for specific mills, therebyachieving maximum results with regard to both economics and efficiency.Furthermore, the novel compositions hereof are effective over a wide pHrange, with all types of pulp and in the presence of fillers and pulpingchemicals. They are the only compositions known to be more effectivethan cationic starch particularly in furnishes containing high amountsof ground wood. They have also been found to be effective in increasingprintability and decreasing linting during the printing of paper madetherewith. They are especially effective in groundwood, newsprint, andeven highly purified chemical pulp. They combine the good properties ofthe acid colloids, i.e., high cationicity, density and retention, withthe dry strength efficiency of acrylamide polymers. As can be seen fromthe previous examples, the novel compositions and process hereofprovides paper with improved tensile strength, internal bonding,bursting, ply-bonding strength, folding endurance, stiffness, sizingcapability and fiber and fines retention.

We claim:
 1. A method of producing dry strength in paper which comprisesapplying to the fibers thereof from about 0.15% to about 5.0%, byweight, based on the weight of the fibers, of an aqueous solution of acopolymer produced by a method which comprises forming an incompleteacid colloid by reacting 1 mole of an acid-soluble, partially condensed,thermosetting, amino-aldehyde resin, in aqueous solution, with fromabout 0.35 to about 1.5 mole of an acid for from about 15 seconds toabout 45 minutes and at a temperature ranging from about 50° C. to about100° C., reacting (1) a water-soluble or water-dispersible, non-anionicacrylamide polymer with (2) said incompletely formed acid colloid forfrom about 15 to about 45 minutes at a temperature ranging from about40° C. to about 100° C., the ratio of (1):(2) ranging from about 4:1 to1:4, by weight, respectively, and at a total solids content of not morethan about 20%, by weight, based on the total weight of the reactionmedia, to thereby form an aqueous solution of a copolymer of said (1)and (2) formation of said acid colloid continuing in the presence ofsaid added acrylamide polymer during said polymer addition.
 2. A methodaccording to claim 1 wherein the amino-aldehyde resin ismelamine-formaldehyde.
 3. A method according to claim 1 wherein theacrylamide polymer is polyacrylamide.
 4. A method according to claim 1wherein the amino-aldehyde resin is melamine-formaldehyde and theacrylamide polymer is polyacrylamide.
 5. A method according to claim 1wherein the molecular weight of the acrylamide polymer ranges from about40,000 to about 500,000.
 6. Paper having a uniform content of from about0.15% to about 5.0%, by weight, of its dry weight, of a copolymerproduced by a method which comprises incomplete acid colloid by reacting1 mole of an acid-soluble, partially condensed, thermosetting,amino-aldehyde resin, in aqueous solution, with from about 0.35 to about1.5 mol of an acid for from about 15 seconds to about 45 minutes and ata temperature ranging from about 50° C. to about 100° C., reacting (1) awater-soluble or water-dispersible, non-anionic acrylamide polymer with(2) said incompletely formed acid colloid from from about 15 to about 45minutes at a temperature ranging from about 40° C. to about 100° C., theratio of (1):(2) ranging from about 4:1 to 1:4, by weight, respectively,and at a total solids content of not more than about 20%, by weight,based on the total weight of the reaction media, to thereby form anaqueous solution of a copolymer of said (1) and (2), formation of saidacid colloid continuing in the presence of said added acrylamide polymerduring said polymer addition.
 7. Paper according to claim 6 wherein theamino-aldehyde resin is melamine-formaldehyde.
 8. Paper according toclaim 6 wherein the acrylamide polymer is polyacrylamide.
 9. Paperaccording to claim 6 wherein the amino-aldehyde resin ismelamine-formaldehyde and the acrylamide polymer is polyacrylamide. 10.Paper according to claim 6 wherein the molecular weight of theacrylamide polymer ranges from about 40,000 to about 500,000.